Non-pgm catalyst for burning carbon soot, and filtration filter and exhaust gas post-processing apparatus using the same

ABSTRACT

The present invention provides a non-PGM catalyst for burning carbon soot without using a noble metal, the non-PGM catalyst comprising: a cerium-praseodymium complex oxide and an iron oxide, the cerium-praseodymium complex oxide impregnated with silver (Ag). The cerium-praseodymium complex oxide illustratively consists of 60 to 95 wt % of cerium oxide and 5 to 40 wt % of praseodymium oxide, and silver (Ag) impregnated in the complex oxide is 1.5 to 3.0 parts by weight of the total weight of the complex oxide. The iron oxide may be an oxide in a form of particles separate from the cerium-praseodymium complex oxide in which silver is impregnated, and may be 0.5 to 2 parts by weight of the total weight of the cerium praseodymium complex oxide.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of KoreanPatent Application No. 10-2011-0103319 filed on Oct. 10, 2011, theentire contents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present invention relates to a non-PGM (platinum-group metals)catalyst for burning carbon soot having an improved oxidizing power at alow temperature, and a filtration filter and an exhaust gaspost-processing apparatus using the same.

(b) Background Art

In recent years, an amount of exhaust gases exhausted from internalcombustion engines are rapidly increasing due to a rapid increase in thenumber of vehicles. In particular, various substances contained inexhaust gases of diesel engines significantly influence the environment,and it is reported that soot in the exhaust gases can cause healthissues, such as allergic disorders or decreased sperm count.

Thus, it is becoming an urgent research project to remove soot inexhaust gases. A commercialized soot removing apparatus includes acasing installed at an intermediate portion of an exhaust pipe connectedto an exhaust manifold of an engine, and a filter (hereinafter, referredto as a “filtration filter”) having fine cells mounted within thecasing.

Then, carbon soot in exhaust gas discharged through an exhaust pipeduring an operation of a vehicle is deposited on cell walls of afiltration filter, so it is necessary to regularly remove the carbonsoot.

As well known in the art, excellent technologies for removing capturedsoot using a catalyst include a passive regeneration method using theoxidizing power of NO₂, and an active regeneration method of removingunburned hydrocarbons produced in an engine by generating oxidation heatin an oxidation catalyst and a filtration filter containing theoxidation catalyst.

In a method of removing captured soot, a high-priced platinum-basedoxidation catalyst (platinum-group metal or PGM) is coated on afiltration filter to lower combustion temperature and improve fuelefficiency.

FIG. 1 is a schematic view for explaining a method of burning carbonsoot by a DPF (Diesel Particulate Filter) catalyst using a PGM catalyst.As illustrated in FIG. 1, carbon soot filtrated by the DPF is burnedwhen NO₂ contained in exhaust gas discharged from an engine and NO₂oxidized by a catalyst, in which platinum (Pt) is coated on analumina/mixture oxide, react with the platinum (Pt).

However, although a combustion temperature can be decreased by using ahigh-priced PGM such as platinum, the price of the catalyst is high,increasing the manufacturing costs of a vehicle.

Meanwhile, Japanese Patent No. 4144898 discloses a soot burning catalystincluding a carrier consisting of a cerium-zirconium complex oxidecontaining 5 to 50 wt % of cerium oxide, and a first catalyst consistingof at least one of silver (Ag) and rubidium (Ru) impregnated in thecarrier or its oxide and having 0.5 to 30 wt % of the carrier.

According to the Japanese patent, soot can be removed at a lowtemperature using an oxidation reaction without using a high-priced PGM.

Although the above Japanese patent discloses an advanced technology,considering that it does not use a PGM, there is still a need to improvea combustion efficiency of soot.

SUMMARY OF THE DISCLOSURE

The present invention provides a non-PGM catalyst which has an oxidizingpower at a low temperature and improves fuel efficiency by decreasingcombustion temperature.

The present invention also provides a filtration filter coated with anon-PGM catalyst having an improved natural regeneration efficiency, andan exhaust gas post-processing apparatus employing the filtrationfilter.

In one aspect, the present invention provides a non-PGM catalyst forburning carbon soot without using a noble metal, the non-PGM catalystcomprising: a cerium-praseodymium complex oxide and an iron oxide, thecerium-praseodymium complex oxide impregnated with silver (Ag), wherebythe non-PGM catalyst which has an oxidizing power at a low temperatureand improves fuel efficiency by decreasing combustion temperature.

In particular, the cerium-praseodymium complex oxide consists of 60 to95 wt % of cerium oxide and 5 to 40 wt % of praseodymium oxide, andsilver (Ag) impregnated in the complex oxide is 1.5 to 3.0 parts byweight of the total weight of the complex oxide.

The iron oxide is an oxide in a form of particles separate from thecerium-praseodymium complex oxide in which silver is impregnated, and is0.5 to 2 parts by weight of the total weight of the cerium praseodymiumcomplex oxide.

In another aspect, the present invention provides a filtration filtercomprising: a plurality of through-cells formed regularly along an axialdirection thereof and partitioned by cell walls, wherein eachthrough-cell has an inlet port and an outlet port opened in oppositedirections at opposite end sides thereof and a carbon soot burningnon-PGM catalyst consisting of a cerium-praseodymium complex oxide(impregnated with silver (Ag)) and an iron oxide is coated on an uppersurface and a lower surface of the cell wall.

The through-cell further comprises a carbon monoxide (CO) oxidizingcatalyst for preventing generation of CO and slippage, the CO oxidizingfilter being coated on a lower surface or an upper surface of the cellwall on which the carbon soot burning non-PGM catalyst or on an entireregion of the lower surface or the upper surface of the cell wall.

In still another aspect, the present invention provides an exhaust gaspost-processing apparatus wherein a DOC (Diesel Oxidation Catalyst)module, an LNT (Lean Nox Trap) module, or a TWC (Three Way Catalyst)module is mounted to an inlet port of a filtration filter coated withthe carbon soot burning non-PGM catalyst consisting of acerium-praseodymium complex oxide and an iron oxide, thecerium-praseodymium complex oxide impregnated with silver (Ag).

Accordingly, the non-PGM catalyst for burning carbon soot, and thefiltration filter and the exhaust gas post-processing apparatus usingthe same have the following advantages.

Since a non-PGM consisting of a cerium-praseodymium complex oxide(impregnated with silver (Ag)) and an iron oxide is applied instead of ahigh-priced PGM, soot can be removed by an oxidation reaction at a lowertemperature and combustion efficiency can be enhanced further ascompared with the conventional technology.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will now bedescribed in detail with reference to certain exemplary embodimentsthereof illustrated in the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of thepresent invention, and wherein:

FIG. 1 illustrates a result of measuring burned carbon soot through aTGA/DSC for various complex oxides, wherein the samples are mixed withtoner carbon (Printex-U) at a ratio of 5 to 1 in a condition of air fluxof 50 ml (containing water);

FIG. 2 illustrates a combustion assisting effect of silver impregnatedin a cerium-praseodymium (80:20) complex oxide, wherein the measurementcondition is the same as the measurement condition of FIG. 1 but dieselengine soot is used instead of toner carbon;

FIG. 3 is a TGA/DSC diagram showing the effect that an iron oxide in theform of second particles contained together with the cerium-praseodymium(80:20) complex oxide has on combustion, wherein the measurementcondition is the same as the measurement condition of FIG. 4;

FIG. 4 illustrates a result of measuring burned carbon soot through aTGA/DSC for various complex oxides applied to the cerium-praseodymium(80:20, A, 90:10, B) complex oxide, wherein the samples are mixed withdiesel engine soot at a ratio of 5 to 1 in a condition of air flux of 50ml (containing water);

FIG. 5 is a view schematically illustrating a state where a soot burningnon-PGM catalyst is coated on a filtration filter according to thepresent invention;

FIG. 6 is an enlarged sectional view of a honeycomb filter where atypical cylindrical ceramic filter catalyst structure is mounted to acasing; and

FIGS. 7 and 8 are views schematically showing apost-processing/purifying system where a DOC or LNT module is attachedto a front end of the filtration filter (0 g/ft3) which does not containa PGM.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will bedescribed with reference to the accompanying drawings so that thoseskilled in the art can easily carry out the invention.

The present invention relates to a non-PGM catalyst which has anoxidizing power at a low temperature and improves fuel efficiency bydecreasing combustion temperature.

The present invention also relates to a filtration filter coated with anon-PGM catalyst having an improved natural regeneration efficiency, andan exhaust gas post-processing apparatus employing the filtrationfilter.

First, some terms used in the specification will be defined hereinbelow,and the terms which are not specifically defined herein can beunderstood as those meanings which are generally used by those skilledin the art.

The term “soot” used herein generally refers to soot materials such ascarbon-containing soot, sulfur-containing soot including sulfides, andpolymer hydrocarbon soot.

The term “filtration filter” used herein includes a trapped (orwall-flow type) filtration filter and an opened (or straight-flow)filter. A representative trapped exhaust gas filter is a honeycombstructure (a diesel PM filter or DPF).

Simply referring to the operation principle of the filtration filter,the honeycomb filter has a plurality of cells extending along its axialdirection, and soot is filtrated by cell walls 10 of the cells whileexhaust gas passes through the filter. As a result, soot is removed fromthe exhaust gas.

Since soot is filtrated and deposited by the cell walls 10 of thehoneycomb filter, pressure loss increases.

The term “pressure loss” used herein refers to a difference betweenexhaust gases at an inlet and an outlet for exhaust gas for the filter.A pressure loss is caused by a resistance due to the soot filtrated onthe cell walls 10 of the filtration filter while exhaust gas passesthrough the filter.

In relation to the filter structure, necessary compositions may becoated on an upper side surface and a lower side surface of the filterwall having honeycombed cells. A “rear side” of the upper side surfaceor lower side surface of the filter wall used herein refers to a cellsection located on an outlet side direction.

A “module” used herein refers to a honeycombed structure on which acertain catalyst is coated to process exhaust gas. For example, a COoxidation module is a honeycombed structure where an oxidizing catalystis coated to expedite a CO oxidation reaction.

A “diesel oxidation catalyst” module used herein is also referred to asa DOC (Diesel Oxidation Catalyst), and refers to a module on whichplatinum (Pt) and/or palladium (Pd) for reducing HC and CO contained inexhaust gas of a diesel engine by 80% are coated as a catalystactivating component.

An “LNT” module used herein refers to a module on which components suchas Ba, Sr, and K for converting exhaust gas into nitrogen and carbondioxide are coated after NOx is filtrated in a lean region with LNT(Lean NOx Trap) and is discharged in a dense region.

A “TWC (Three-Way Catalyst)” module used herein refers to a module onwhich exhaust gas CO and HC are coated in an oxidation reaction and NOxis coated in a reduction reaction, whereby a three-way catalyst iscoated.

1. Soot Burning Catalyst

The non-PGM catalyst 11 for burning soot according to the presentinvention, in particular, the non-PGM catalyst which does not use a PGMconsists of cerium-praseodymium complex oxides where silver (Ag) isimpregnated and iron oxides.

That is, the complex oxide particles where a silver component isimpregnated and the iron oxide particles are mixed to form a catalyst.

The cerium-praseodymium complex oxide consists of 60 to 95 wt % of acerium oxide and 5 to 40 wt % of a praseodymium oxide, and the silvercomponent impregnated in the complex oxide is 1.5 to 3.0 parts by weightof the total weight of the complex oxide.

The iron oxide is an oxide in a form of particles separate from thecomplex oxide, and is 0.5 to 2 wt % of the total weight of the complexoxide.

The composition ratio of the metals and/or the oxides of the catalyst istotally based on experiments. FIG. 1 illustrates a preliminaryexperiment result for identifying components of complex oxides whichexhibit efficient combustion results.

In the graph of FIG. 1, DSC is an acronym for Differential Scanningcalorimeter.

That is, an optimum complex oxide components and a composition ratio ofFIG. 1 can be obtained by comparing a complex oxide (A) of 80 wt % of Ceand 20 wt % of Pr and a complex oxide (B) of 90 wt % of Ce and 10 wt %of Pr with various compositions and measuring soot burning capacities.

For example, the composition disclosed in Japanese Patent No. 4144898,i.e., the cesium-zirconium based complex oxide has a combustiontemperature of approximately 500° C., but the cerium-praseodymiumcomplex oxide can burn soot at a temperature of 530° C., which is asurprising result.

Silver of 1.5 to 3.0 parts by weight of the total weight of the complexoxide is impregnated in the cerium-praseodymium complex oxide.

FIG. 2 is a TGA/DSC diagram showing a silver impregnating effect.

In this case, TGA is an acronym of ThermoGravimetric Analysis.

That is, when 0.1 to 4.0 wt %, preferably 2.5 wt % of silver isimpregnated in the cerium-praseodymium (80:20) complex oxide, combustiontemperature becomes lowest, making it possible to further enhancecombustion effect.

Without being limited to the theory, the silver impregnated in thecomplex oxide is recognized as a component for maximizing active oxygenspecies advantageous in oxidation of carbon soot.

The active oxygen species oxidize carbon soot to CO or CO₂ through apartial or full oxidation reaction.

However, surprisingly, the silver component does not increase combustioneffect in proportion to an amount of the silver component added to thecomplex oxide, but forms a constant point of inflection in combustioneffect. According to the present invention, when 2.5 wt % of silver isimpregnated in the cerium-praseodymium (80:20) complex oxide, aninflection point of combustion efficiency is formed (see FIG. 2).

Moreover, the non-PGM catalyst 11 for burning carbon soot according thepresent invention further comprises an iron oxide together with an Agimpregnated cerium-praseodymium complex oxide.

According to one or more embodiments of the present invention, the ironoxide is provided not in the form of a complex oxide integrally formedwith the cerium-praseodymium complex oxide but in the form of separateparticles.

That is, the combustion catalyst according to the present invention mayhave a form where the complex oxide particles in which the silvercomponent is impregnated and the iron oxide particles are physicallymixed.

The iron oxide has 0.5 to 2 wt % of the total weight of the complexoxide.

FIG. 3 is a TGA/DSC diagram showing a combustion effect due to additionof an iron oxide. That is, if 1.0 wt % of the iron oxide is impregnatedin the cerium-praseodymium (80:20) complex oxide, the combustion effectis further enhanced. However, if 3 wt % of the iron oxide isimpregnated, the combustion effect is further reduced.

As an inflection point in the combustion effect exists in an amount ofsilver (Ag), it can be seen from FIG. 5 that an inflection point incombustion efficiency can be formed when approximately 2 wt % or more ofthe iron oxide is contained in the complex oxide.

FIG. 4 is a graph obtained by measuring an activity of a catalystconsisting of a silver (Ag) impregnated cerium-praseodymium complexoxide.

That is, when silver (Ag) is impregnated in the cerium-praseodymiumcomplex oxide and the iron oxide is mixed with the complex oxide, asynergy effect due to Ag and the iron oxide can be obtained.

It can be seen from FIG. 4 that the catalyst containing the silverimpregnated cerium-praseodymium complex oxide and the iron oxideenhances combustion efficiency due to the unexpected synergy effect dueto the silver component and the iron oxide as compared with thecerium-praseodymium complex oxide, the silver impregnatedcerium-praseodymium complex oxide, or the cerium-praseodymium complexoxide containing the iron oxide.

2. Soot Filtration Filter

As illustrated in FIG. 5, the filtration filter according to the presentinvention may have a soot burning non-PGM catalyst coated on an uppersurface and a lower surface of a filter wall.

To achieve this, the soot burning non-PGM catalyst 11 may furthercomprise silica or alumina as a binder component.

The filter applied to the present invention is not specifically limited,but a soot filtrating honeycomb filter for a diesel engine isexemplified for simplicity.

FIG. 6 is an enlarged sectional view of the honeycomb filter where atypical cylindrical ceramic filter catalyst structure 21 is mounted to acasing 20.

The ceramic filter catalyst structure has a plurality of through-cells22 having a substantially square shape and formed regularly along anaxial direction thereof, and the through-cells 22 are partitioned bythin cell walls 10.

In this case, the entire cross-section of the filter structure has ashape of a chess board.

Generally, the density of the cells is designed to be approximately 200to 300 cells/in², and the thickness of the cell wall 10 is approximately0.3 mm.

A plurality of inlet ports 23 are formed on one side of the plurality ofthrough-cells 22 and a plurality of outlet ports 25 are formed on anopposite side thereof. The inlet ports 23 and the outlet ports 25 areopened in opposite directions, and the opposite sections of the inletports 23 and the outlet ports 25 are sealed by a sealing material 14.

The soot burning non-PGM catalyst 11 according to the present inventionis coated on the upper or lower surface of the cell wall 10.

Although a catalyst coating method has been illustrated, the presentinvention is not limited thereto.

In the catalyst coating method according to the embodiment of thepresent invention, the catalyst powder according to the presentinvention forms a slurry together with a binder component such asalumina sol and water.

The slurry is coated on the filter cell wall 10 through a generaldipping method and is plasticized.

In order to prevent generation of CO and slippage which can bepotentially generated due to an incomplete oxidation reaction of thenon-PGM combustion catalyst according to the present invention, the sootfiltration filter of the present invention is further coated with the COoxidation catalyst 12 consisting of a platinum-based element on anentire region of a lower or upper surface of the cell wall 10, or asection of the outlet side on a side opposite to the soot burningnon-PGM catalyst 11 (see FIG. 5).

Alternatively, the soot filtration filter of the present invention mayhave a CO oxidation catalyst 12 module spaced apart from or in contactwith a rear end of the filter.

3. Exhaust Gas Post-processing System According to the presentinvention, as illustrated in FIGS. 7 and 8, an exhaust gaspost-processing/purifying system where a DOC 30 module, an LNT 20module, or a TWC module is mounted to an inlet port of the filtrationfilter coated with the non-PGM catalyst is provided.

The DOC 30, LNT 31, and TWC modules correspond to the modules of theexhaust gas post-processing/purifying system generally understood bythose skilled in the art.

Hereinafter, the present invention will be described in more detail withreference to the following embodiment, but the present invention is notlimited to the embodiment.

Exemplary Embodiment

First, after silver nitrate as an Ag precursor is diluted with a largeamount of distilled water, it is impregnated in CePrO₂ (80:20) powder(A), is dried at 120° C. for four hours, and is plasticized at 450° C.for two hours to manufacture an AG/CePrO₂ (2.5 wt % Ag/A).

Al₂O₃ is mixed with the complex oxide with Fe₂O₃ powder (1.0 wt %) and abinder and the mixture is wet-milled to an average particle size of 7 μmto manufacture a slurry.

The manufactured slurry is impregnated in the DPF in a dipping method,is dried at 120° C., and is plasticized at 450° C. for one hour tofinish the filtration filter of the present invention.

Comparison Examples

A commercial filtration filter where a PGM is applied as a catalyst isused.

The PGM used in the comparison example has a density of 26.7 g/ft³ andhas a ratio of 2Pt/lPd.

Comparison Example 1 uses a filtration filter where a high-density PGMis coated at a front end section of the DPF cell wall and a low-densityPGM is coated at a rear end section of the DPF cell wall, ComparisonExample 2 uses a filtration filter where a intermediate-density PGM iscoated at the entire section of the DPF cell wall, and ComparisonExample 3 uses a filtration filter where a intermediate-density PGM iscoated at the entire section of the DPF cell wall.

Experimental Example of Engine

After being aged at 800° C. for 10 hours, the filtration filter is hungat a rear end of the DOC. The carbon soot is loaded at 8 g/L (an amountof filtrated carbon soot per unit volume of the filtration filter) in atransient mode where an engine condition (RPM and torque) simulating anactual road travel is changed, and the engine condition for evaluationof regeneration is set to a target temperature of 620° C. and 560° C. soas to control an inlet temperature of the filtration filter throughcontrol of a post-injected amount of an engine at 2000 RPM/40 Nm.

The regeneration efficiency of carbon soot is determined by a DPF weightbefore the experiment and a DPF weight after the regeneration, and theregeneration efficiency at 620° C. and the regeneration efficiency at560° C. are listed in Tables 1 and 2 respectively.

TABLE 1 Soot Regeneration Efficiency (%) Constitution of Catalyst at DPF620° C. Embodiment (non-PGM) 80.5 Comparison Example 1 75.9(high-density and low-density PGM) Comparison Example 2 78.4(intermediate-density PGM) Comparison Example 3 87.4(intermediate-density PGM)

TABLE 2 Soot Regeneration Efficiency (%) Constitution of Catalyst at DPF560° C. Embodiment (non-PGM) 49.0 Comparison Example 1 25.0(high-density and low-density PGM) Comparison Example 2 46.0(intermediate-density PGM) Comparison Example 3 54.0(intermediate-density PGM)

As listed in Tables 1 and 2, the soot burning non-PGM catalyst accordingto the present invention shows a result corresponding to the commercialfiltration filters to which PGMs are applied in the actual engineexperiments.

That is, considering that the conventional filtration filters containPGMs and their prices are high, the soot burning non-PGM catalyst whichcan be manufactured at low costs according to the present inventionshows a considerably improved combustion efficiency.

Thus, according to the present invention, since a non-PGM consisting ofa cerium-praseodymium complex oxide (impregnated with silver (Ag)) andan iron oxide is applied instead of a high-priced PGM, soot can beremoved by an oxidation reaction at a lower temperature and combustionefficiency can be enhanced further as compared with the conventionaltechnology.

What is claimed is:
 1. A non-PGM catalyst for burning carbon sootwithout using a noble metal comprising: a cerium-praseodymium complexoxide impregnated with silver (Ag); and an iron oxide, wherein thecerium-praseodymium complex oxide consists of 60 to 95 wt % of ceriumoxide and 5 to 40 wt % of praseodymium oxide, and silver (Ag)impregnated in the complex oxide is 1.5 to 3.0 parts by weight of thetotal weight of the complex oxide.
 2. The non-PGM catalyst of claim 1,wherein the iron oxide is an oxide in a form of particles separate fromthe cerium-praseodymium complex oxide in which silver is impregnated,and is 0.5 to 2 parts by weight of the total weight of the ceriumpraseodymium complex oxide.
 3. The non-PGM catalyst of claim 1, furthercomprising silica or alumina as a binder component.
 4. A filtrationfilter comprising: a plurality of through-cells formed regularly alongan axial direction thereof and partitioned by cell walls, wherein eachthrough-cell has an inlet port and an outlet port opened in oppositedirections at opposite end sides thereof, and a carbon soot burningnon-PGM catalyst consisting of a cerium-praseodymium complex oxide andan iron oxide coated on an upper surface and a lower surface of the cellwall, the cerium-praseodymium complex oxide impregnated with silver(Ag).
 5. The filtration filter of claim 4, wherein the through-cellfurther comprises a CO oxidizing catalyst for preventing generation ofCO and slippage, the CO oxidizing filter being coated on a lower surfaceor an upper surface of the cell wall on which the carbon soot burningnon-PGM catalyst or on an entire region of the lower surface or theupper surface of the cell wall.
 6. The filtration filter of claim 4,wherein each through-cell further comprises a CO oxidizing catalystcoated on a portion of the cell wall on a side of the outlet port. 7.The filtration filter of claim 4, wherein a honeycombed CO oxidizingcatalyst module on which the CO oxidizing catalyst is coated is furthermounted to a side of the outlet port of the filtration filter.
 8. Anexhaust gas post-processing apparatus wherein one of a DOC (DieselOxidation Catalyst) module, an LNT (Lean Nox Trap) module, or a TWC(Three Way Catalyst) module is mounted to an inlet port of a filtrationfilter coated with a carbon soot burning non-PGM catalyst consisting ofa cerium-praseodymium complex oxide and an iron oxide, thecerium-praseodymium complex oxide impregnated with silver (Ag).